Shorted out the red & white wires at furnace to eliminate the thermostat. Unit turns on for 5-6 minutes & then the burners shut off, fan remains on for 1 minute, & then shuts off. Since wires are shorted the electronic ignition starts up again & the 5-6 minutes process repeats.

Sounds like a fan or hi-limit problem, I would go with the fan or the control for fan.